The hydrogenation of α,β-unsaturated ketones by hydrogen is known. The hydrogenation of ketones having at least a carbon-carbon double bond in the γ,δ-position to the keto group (=γ,δ-unsaturated ketones), however, differs strongly as the keto group and the double bond do not form a conjugated system. The carbon-carbon double bond is known in a majority of cases to be prochiral so that upon hydrogenation chiral centre(s) may be formed.
Hydrogenation products of such ketones having at least one carbon-carbon double bond play an important role particularly in the field of synthesis of vitamins, particularly of vitamins E and K1. However, traditional known hydrogenations of such γ,δ-unsaturated ketones are unspecific and, hence, lead to formation of mixtures of isomers, the number of which dramatically increases as the number of chiral centres being formed by hydrogenation increases.
The (biological) activities of vitamins, however, are contributed mainly to only one or a few isomers out of the plurality of isomers. Hence, there exists a large interest to offer a method of hydrogenation allowing a selective formation of primarily one single isomer.
WO 2006066863 deals with the hydrogenation of alkenes using chiral iridium complexes. These chiral iridium complexes show a particularly good selectivity in the hydrogenation of olefins.
A large variety of chiral iridium complexes are disclosed in Chem. Sci., 2010, 1, 72-78 where a large variety of trisubstituted olefins are hydrogenated in a asymmetrical manner. Apart from purely hydrocarbon substituted olefins, only certain ether, ester or hydroxyl functionalized olefins are disclosed to be hydrogenated by the use of said iridium complexes.